Long-Term Planting of Taxodium Hybrid 'Zhongshanshan' Can Effectively Enhance the Soil Aggregate Stability in Saline-Alkali Coastal Areas

Not enough research has been conducted on the mechanisms influencing the stability of soil aggregates in coastal saline-alkaline soil and the dynamic changes in aggregates in the succession process of coastal saline-alkaline soil brought on by longer planting times. In this study, soil aggregate composition, stability, and influencing factors of 0-20 cm, 20-40 cm, and 40-60 cm soil layers in different planting time stages were analyzed in the reclaimed land at the initial stage of afforestation and the Taxodium hybrid 'Zhongshanshan' plantation with planting times of 6, 10, 17, and 21 years. The results show that, with the increase in planting time, the aggregate stability of the plantation increased significantly. In the 0-20 cm soil layer, the geometric mean diameter (GMD) and aggregate size >0.25 mm (R-0.25) increased by 81.15% and 89.80%, respectively, when the planting time was 21 years, compared with the reclaimed land. The structural equation (SEM) showed that planting time had a direct positive effect (path coefficient 0.315) on aggregate stability. However, soil sucrase (0.407) and beta-glucosidase (0.229) indirectly improved the stability of aggregates by affecting soil organic carbon. In summary, the establishment of Taxodium hybrid 'Zhongshanshan' plants on coastal saline-alkali land is beneficial for stabilizing soil aggregates, improving soil structure, and boosting soil quality. Long-term planting of Taxodium hybrid 'Zhongshanshan' can be an effective measure for ecological restoration in this region.